The invention relates to a method for the production of a steel strip, more particularly, a steel strip having a thickness of 2-25 mm, wherein a strand is cast in a cooled oscillating continuous chill mould, the strand leaving the continuous chill mould with solidified strand shells and liquid core is squeezed together, more particularly, to a thickness of 40-50 mm at least until the strand shells are welded, and then the strand is hot rolled in the casting heat to a thickness of 2-25 mm.
Thin steel strips of high quality can be produced comparatively inexpensively by such a method, as shown from EP 0286862 A1. In that method, squeezing together is performed by a pair of squeezing rolls disposed immediately downstream of the chill mould. Thereafter the strand is rolled down with a degree of deformation of 5-85% to the strip thickness of 2-25 mm.
In that method, due to the different heat transfers during the cooling of the strand in the continuous chill mould, strand shells of locally different thicknesses may be formed. If such a strand is squeezed together by the squeezing rolls disposed downstream of the chill mould until the strand shells have become welded, a strand may be produced which has across its width not only different temperatures, but also different thicknesses and structures. These local differences across the strand width lead to different deformation resistances of the material, so that when rolling-down is performed by the squeezing rolls, because of fibres of different length, the strip emerging from the roll nip appears wavy in the longitudinal direction, when viewed over the width. If the material has different lengths at the opposite strip edges, the result is that the strip takes on a cambered course--i.e., deviates from a straight run-out. Strips which deviate from a straight run-out cause processing difficulties in the connected processing units, such as high deformation roll stands and coilers.
To control the straight run-out of rolled strips., it is known from U.S. Pat. No. 3,491,562 to determine the deviation of strip running from a straight run-out downstream of a roll stand and, in case of deviation, to adjust the nip section of the preceding roll stand in the sense of a correction of strip running. This correction of strip running inevitably results in an alteration of the thickness of the strip across its width. When a strip having a low degree of deformation is rolled, the different strip thickness may be acceptable; but with substantially higher degrees of deformation, up to 85%, this kind of correction of strip running would cause unacceptable differences in thickness across the strip width, more particularly, because the connected high deformation rolls require a given strip run-in cross-section. This way of correcting strip running is therefore unsuitable for a method of the kind specified initially.